System for the reconstruction of symmetrical body parts

ABSTRACT

A medical system for assisting in the planning and/or performance of the reconstruction of normally symmetrical body parts of a patient comprises a measuring unit for measuring a first surface and a second surface for determining a topography of the first and second surfaces, a storage unit for storing the determined topographies of the first and second surfaces, an evaluation unit for establishing a mirror image of the stored topography of the first surface and for calculating deviations of the stored topography of the second surface from the first surface mirror image, and a control unit for outputting guidance information for at least one medical instrument on the basis of the calculated deviations of the topography of the second surface, in order to reconstruct the topography of the second surface according to the mirror image of the topography of the first surface.

The invention relates to a system for assisting in planning and/orperforming the reconstruction of usually symmetrical body parts of apatient.

In invasive surgical interventions, surgical instruments are moved in anoperating region in the body of a patient by a surgeon during anoperation. An operating region refers to the space in the interior ofthe patient which is potentially or effectively affected by the employedsurgical instruments during the operation. The operation includes theinsertion and removal of surgical instruments into the body of thepatient and out of the body of the patient, as well as the movement ofthe surgical instruments within the body of the patient and the use ofthe surgical instruments in an intervention region which is arranged inthe operating region and precisely predefined. The intervention regionrefers to the part in the operating region which is to be worked on bythe surgeon. By way of example, this can relate to the tissue to beremoved or vessels to be closed. Accordingly, an operating region maycomprise a plurality of intervention regions. A multiplicity ofsensitive structures lie next to the intervention regions in theoperating region and they are to be preserved from damage by thesurgical instruments. The sensitive structures include, for example,vessels, organs, nerves, muscles, ligaments, sinews and other, generallyintact tissue which is intended to be maintained in order to restrictthe effects of the operation to a necessary minimum, as any furtherimpairment of the body of the patient during the operation may increasethe health risk to the patient and have a negative influence on theresult of the operation.

Tumor diseases, accidents or defects present at birth often requirereconstruction of the tissue of the patient, in so doing, functional andaesthetic aspects are to be taken into account when rebuilding the boneand soft tissue structure of the patient, particularly in the facialregion. In the case of such interventions in the face of the patient, itis particularly important for the face to have symmetry that is as exactas possible after the operation, as even slight deviations from thesymmetry are already clearly perceivable and may constitute a permanentfunctional and also psychological burden for the patient.

When planning the rebuilding or reconstruction of the bone and softtissue structure of the face of the patient, the plane of symmetry ofthe face is usually established first. To this end, the geometricsituation of the face is detected by means of optical methods, e.g. onthe basis of pattern projection or a laser distance measurement. Usingvarious methods, the plane of symmetry can be determined automaticallyfrom the surface structure of the face established therewith. In asubsequent step, the surface structures of the two sides separated bythe plane of symmetry are established, compared to one another and hencedifferences are established. This is generally carried out by means ofcomplicated CAD programs, which are only designed for particularlyhighly trained users.

Moreover, systems for the navigation on the basis of the bone structuresare known and used, e.g. in the case of surgical interventions on thespinal column or in the field of ENT. Such systems generally comprise aposition detection system for detecting the positions of medicalinstruments and of the patient in a reference coordinate system and aguidance system for provision of guidance data for navigating thesurgical instruments. By coordinating the guidance of the medicalinstruments, conventional navigation systems significantly unburden thesurgeon, as this object requires a large degree of spatial imagination.Accordingly, the risk of the operation is lowered and the results of theoperation are improved.

In known navigation or position detection systems, the instrument orpatient position is usually determined on the basis of optical orelectromagnetic methods, with systems with optical methods being morecommon. In conventional electromagnetic methods, the position of themedical instruments is measured in an alternating electromagnetic fieldgenerated by a field generator by way of the strength of currents whichare induced in a position sensor that is arranged at the medicalinstrument. It is well known that position sensors suitable herefor havea plurality of coils, in particular three coils. However,electromagnetic position detection systems are disadvantageous in thatpossible error sources, such as e.g. active surgical instruments whichlikewise emit an electromagnetic field during operation, need to bedetected and compensated for.

Known measuring and navigation systems are all disadvantageous in thatthey cause relatively high procurement costs, often have greatcomplexity and can only be operated by specifically trained specialists.Furthermore, these systems are often cumbersome in terms of handling andtherefore provide a multiplicity of potential error sources. Moreover,these systems all require image data of the patient and therefore need along preparation time and may, in certain circumstances, lead toadditional radiation exposure of the patient.

Therefore, it is the object of the present invention to provide a methodand a system planning and performing the navigation when rebuildingsymmetrical body parts of the patient, which do not have theaforementioned disadvantages.

According to the invention, this object is achieved by a medical systemfor assisting in planning and/or performing the reconstruction ofusually symmetrical body parts. The system comprises at least onemeasuring unit for measuring a first area and a second area in order toestablish a topography of the first area and the second area. This canrelate to areas or surfaces of a patient, wherein the areas are selectedto satisfy the criterion that the first area in a healthy human isusually substantially mirror symmetrical in relation to the second area.Furthermore, provision is made of a storage unit for storing theestablished topographies of the first area and the second area of thepatient. The system moreover has an evaluation unit for establishing amirror image of the stored topography of the first area and forcalculating deviations between the stored topography of the second areaand the mirror image of the stored topography of the first area, as wellas a control unit for outputting guidance information for at least onemedical instrument on the basis of the calculated deviations in thetopography of the second area from the mirror image of the storedtopography of the first area in order to reconstruct the topography ofthe second area in accordance with the mirror image of the topography ofthe first area. Using a system according to the invention, a topographyof two symmetry halves of usually symmetrical body parts isestablishable. If a symmetry half to be treated has an ACTUAL topographywhich has asymmetries in relation to the corresponding intact symmetryhalf, an INTENDED topography can be established by mirroring thetopography of the corresponding intact symmetry half for the purposes ofproducing or reconstructing the symmetry of the symmetry half to betreated.

Guidance information for controlling at least one medical instrument isgenerable from the deviations between the ACTUAL topography and theINTENDED topography.

Preferably, the medical system has a data transmission interface fortransmitting the topography data of a surface established by themeasuring unit to the evaluation unit and/or storage unit. In this case,the measuring unit can be connected by cables or comprise a radio devicefor transmitting the measured values.

In a first embodiment of the invention, at least, one measuring unitcomprises a mechanical sensing device for mechanically sensing an area.By way of example, the sensing device can comprise a pointer with aninstrument handle and an instrument tip for sensing the area orindividual measurement points. The sensing device can be integrated in aposition detection system such that position data from a sensing tip ofthe sensing device are establishable by the position detection systemand displayable on a display unit. Using such a sensing device, theposition of individual measurement points of an area is detectable inthe coordinate system of the position detection system and hence thetopography of the area is establishable by mechanical sensing.

Particularly preferably, the mechanical sensing device comprises apointer with an at least partly spherically shaped instrument tip. Suchinstrument tips are advantageous in that they can be guided well over anarea of the patient in a sliding manner, without injuring the area.Alternatively, pointers with a pointed or conical instrument tip areusable, particularly for sensing individual measurement points, since apoint can be actuated more precisely using such an instrument tip.

In a second embodiment of the invention, at least one measuring unitcomprises an optical sensing device for optically sensing an area: Inthe process, light waves are emitted and reflections and/or shadowformations are detected using optical means. Conclusions about theembodiment of the topography of the respective area can be drawn fromthe results.

Preferably, the optical sensing device comprises a laser and/or a videodevice and/or a photocell. Particularly preferably, the image dataestablished by the optical sensing device are displayable on a displayunit such as e.g. a monitor.

Particularly preferably, the system is embodied to automaticallyidentify natural symmetries on the basis of recordings, e.g. photos. Tothis end, the system can have a detection unit, for example an opticalreading unit, which can acquire a recording which: comprises both thefirst area and the second area to be reconstructed. The system canestablish INTENDED lines of symmetry from the acquired recording and, ina second step, preferably: also establish the deviation of the ACTUALtopography of the second area from the INTENDED topography—the mirrorimage of the first area—thereof. To this end, use is preferably made ofstereoscopic recordings, 3D recordings or else of models produced bytomography.

The evaluation unit can be embodied to take into account possibleswellings of tissue in the tissue situated in the region of the secondarea when calculating deviations between the stored topography of thesecond area and the mirror image of the stored topography of the firstarea. What can be achieved thereby is that, post surgery, a second areato be reconstructed has desired topography after detumescence of thetissue situated in the region of the second area. Swelling of the tissuecan, for example, be taken into account by a supplemental value added toa sensed value established by optical or mechanical means. Thesupplemental value can be formed by a height difference between theswollen and detumescent state of the tissue. By way of example, adetumescent state can be predicated by a tissue model which can bestored in the evaluation unit. By way of example, the tissue model caninclude a skin tension characteristic, which is preferably establishedby optical and/or mechanical means. More preferably, the system isembodied to measure the topography of naturally symmetrical cavities,wherein a first cavity comprises the first area and a second cavitycomprises the second area.

Alternatively or additionally, the evaluation unit can be embodied tonecessarily include points of the topography of the second area definedas intact when producing the mirror image of the stored topography ofthe first area. By way of example, junctions of a bone, particularly onesituated in, or in the vicinity of, the region to be reconstructed, canbe defined as intact points. As a result, the mirror image of the storedtopography of the first area can thus he deformed imperfectly, i.e. itcan be asymmetrical in relation to the topography of the first area,particularly in the region of the junction of a bone. Thus, by way ofexample, in the case of a left upper jaw half to be reconstructed (inwhich the second area lies) on the basis of a right upper jaw half (inwhich the first area lies) with an axis of symmetry situated in theanterior apposition surface, the left cheekbone can be defined as anintact junction. Since the human face is typically slightlyasymmetrical, an offset would emerge between the left upper jaw half andthe left cheekbone in the case of perfect mirroring of the right upperjaw half about the axis of symmetry situated in the anterior appositionsurface. By defining the left cheek bone as an intact junction, thisjunction is now included by the evaluation unit when producing themirror image of the stored topography of the first area. The mirrorimage of the stored topography of the first area is now distorted in theregion of this junction such that the left upper jaw half can bereconstructed without offset in relation to the left cheekbone.

In an advantageous embodiment of the invention, at least one medicalinstrument is embodied as a balloon catheter. In accordance with theguidance information output by the control unit, the balloon catheter isfillable with a work fluid. The process of filling the balloon catheteris preferably controllable automatically by the medical system, and so amanual intervention by the surgeon is substantially only necessary inemergencies. To this end, the medical system particularly preferably hasa connector for the work fluid or a corresponding pressure generator,such as e.g. a compressor.

Preferably, the system has at least one sensor for detecting theinternal pressure and/or the extent of the balloon catheter.Conventional pressure sensors for fluids are suitable as a sensor forestablishing the internal pressure of the balloon catheter. By way ofexample, measuring the extent of the balloon catheter can be carried outby way of strain gauges. A plurality of strain gauges, each arranged inthe direction of one of the strain components to be determined, areprovided for establishing the multi-axis extent of the balloon catheter.Particularly preferably, at least two strain gauges have an angle of 90°in relation to one another.

It is furthermore preferable for the data acquired by the sensor to betransmittable to the control unit by way of a sensor data interface.

More preferably, the control unit is embodied to control the filling ofthe balloon catheter taking into account the data established by thesensor. Hence, the control unit can terminate the filling of the ballooncatheter once the balloon catheter has a desired extent.

Preferably, the control unit is embodied to control a filling speed ofthe balloon catheter in a manner dependent on the respective extentand/or on the internal pressure of the balloon catheter, wherein thefilling speed is tendentiously intended to decrease with increasingextent or with increasing internal pressure of the balloon catheter.Hence, a load on, and possible damage to, the tissue to be produced orto be reconstructed can be reduced.

In an advantageous embodiment of the invention, the balloon catheter hasa plurality of chambers, wherein the chambers are fillable independentlyof one another. As a result of this, geometries that are morecomplicated can be obtained using a balloon catheter since theindividual chambers are fillable to a different extent, according torequirements.

Preferably, the evaluation unit is configured to establish deviations inthe topography of the second area from the mirrored topography of thefirst area on the basis of individual representative measurement pointson the second area. Accordingly, there is no need to measure amultiplicity of measurement points which are arranged between tworepresentative measurement points or the position of which need not bechanged within the scope of the production or reconstruction. As aresult, the number of measurement points to be sensed in the second areais significantly reducible. As a result of this, there is alsosignificant reduction in the impairment or risk of injury to the patientand in the work complexity during sensing.

Particularly preferably, the measuring unit is embodied to establish thetopography of the second area, at least at representative measurementpoints, during the production or reconstruction of the second areahence, the progress of the intervention can be established during theprocess of producing or reconstructing the second area.

More preferably, the control unit adapts the guidance information for atleast one medical instrument on the basis of the topography data of thesecond area established during the reconstruction of the second area. Inthe case of unpredictable deviations in the topography of the secondarea from corresponding intended values, the expansion of the ballooncatheter, for example, can be automatically stopped by the control unitin order to prevent injury to the patient.

In an advantageous embodiment of the invention, the medical instrumentis an active medical instrument, wherein the control unit is embodied tocontrol the operating state of the active medical instrument in a mannerdependent on the position of the active medical instrument from thetopography of the second area established by the control unit.Therefore, it is possible to stop, i.e., for example, switch off, anactive medical instrument, e.g. a cutting instrument, when theinstrument tip is arranged at a point in the established topography ofthe second area at which no cut is intended to be carried out.Accordingly, the active medical instrument can be put into the active.operating state, or remain therein, when the instrument tip is arrangedat a point in the established topography of the second area, at which acut is intended to be performed. Provision can likewise be made forturning down the active medical instrument when it approaches a point atwhich no cut is intended to be performed and for increasing theoperating state of the active medical instrument when it moves away fromsuch a point.

Below, the invention is intended to be explained in more detail on thebasis of an exemplary embodiment, with reference being made to adrawing. Herein:

FIG. 1 shows an embodiment of a medical system for assisting in planningand/or performing the reconstruction of usually symmetrical body partsof a patient; and

FIG. 2 shows a magnified side view of a balloon catheter from FIG. 1with pressure chambers.

The exemplary embodiment system according to the invention imaged inFIG. 1 comprises an evaluation unit 36, a storage unit 30, a controlunit 28, a pointer 10, a field generator 40, a balloon catheter 20 witha fluid compressor 24, and a display unit 32.

The pointer 10 is connected to the evaluation unit 36 by way of aninstrument cable 44 and has a proximal instrument handle 12, a sphericalinstrument tip 18, an instrument shaft 14 arranged coaxially with theinstrument handle 12 between the instrument handle 12 and the instrumenttip 18, as well as an instrument sensor 16, which is arranged at theinstrument shaft 14 in this embodiment. Alternatively, the instrumentsensor 16 can also be arranged at the instrument tip 18. As analternative to the spherical form, the instrument tip 18 can, forexample, also have a conical, tetrahedral or pyramid shape, with thepointed part preferably pointing in the distal direction. Using theinstrument tip 18, it is possible to sense an area of a patient,registered in the position detection system, in a line-shaped orpoint-shaped manner. Prior to this, the patient needs to be registeredin the position detection system so that the position of the patient isknown in the coordinate system of the position detection system. To thisend, a patient localizer (not depicted here) is arranged in an immovablemanner on the patient, with currents being induced in the patientlocalizer in a manner dependent on the position of the patient localizerin respect of the field generator 40. These currents are measurable bythe evaluation unit 36. The patient is registrable in the positiondetection system by way of a sensing process of individualrepresentative points on the body of the patient using the pointer 10.

During the sensing procedure of the area of the patient registered inthe position detection system, the pointer 10 is guided either in amanner sliding over the area or directly to individual measurementpoints. The measurement points are preferably to be selected in such away that they represent specific points in the area, e.g. protrudingbones. In the case of sliding guidance, the position data of theinstrument tip 18 can be detected continuously by the evaluation unit 36and stored in the storage unit 30. In the case of direct actuation ofindividual measurement points, at least the location of the instrumenttip 18 when reaching the measurement point is to be detected and stored.By way of appropriate software, areas lying between two points can bereconstructed by calculation. In this manner, a topography of the sensedarea of the patient is establishable and storable.

The location of the instrument tip 18 is determined by way of a positiondetection system integrated into the evaluation unit 36. The fieldgenerator 40 is connected by way of a generator cable 38 to theevaluation unit 36 and controlled by the latter. The field generator 40emits an alternating electromagnetic field 42 which, in a mannerdependent on the location of the instrument sensor 16 relative to thefield generator 40, induces currents in the instrument sensor 16.Preferably, the instrument sensor 16 has three coils, and so threecurrents are induced. The current strengths are measured by theevaluation unit 36 and hence the position of the instrument sensor 16 isdetermined relative to the field generator 40. If the pointer 10 waspreviously registered in the position detection system, the position ofthe instrument tin 18 is also known thus.

The evaluation unit 36 may have software, by means of which symmetricalareas are identifiable and axes of symmetry are establishable.Alternatively, the axes of symmetry can also be defined manually, forexample by way of appropriate marking of points lying on an axis ofsymmetry with the aid of the pointer 10. The evaluation unit 36 isconfigured to mirror the topography of a first area, which is referredto as reference area, by way of the axis of symmetry and to compare themirror image of the topography of the first area with the topography ofa second area, with the topography of the second area ideally alreadycorresponding to the topography of the mirrored first area in respect ofposition and form. To the extent that the topography of the second areadeviates from the mirror image of the topography of the first area, theevaluation unit 36 can establish the difference between the two areasand, from this, determine a correction value which can be forwarded tothe control unit 28. On the basis of the correction value, the controlunit 28 can control the filling of the balloon catheter 20 by means ofthe fluid compressor 24 and a catheter tube 22, which connects the fluidcompressor 24 to the balloon catheter 20. The fluid compressor 24 isconnected to the control unit 28 by way of a compressor cable 26.

Various image data of the patient, medical instruments and prosthesesare displayable on the display 32, which is connected to the evaluationunit 38 by way of a display cable 34. Said image data can refer to theimage data obtained both prior to surgery and also during surgery, whichimage data are imageable separately next to one another on virtualscreens or in a superposed manner on one screen. Particularly in thecase of the superposed representation, it is important that allsuperposed objects are registered in the position detection system suchthat position and location of the individual objects can be assigned tothe reference coordinate system of the position detection system. Inthis example, the display 32 is a monitor.

The balloon catheter 20 from FIG. 1 is imaged in a magnified side viewin FIG. 2 and it has a first chamber 20 a and a second chamber 20 b,wherein the first chamber 20 a and the second chamber 20 b are fillableseparately from one another by way of a first channel 22 a and a secondchannel 22 b, respectively, of the catheter tube. Strain gauges 46 arearranged on the balloon catheter 20 in a manner distributed along theouter circumference, wherein some strain gauges 46 are aligned parallelto and some strain gauges 46 are aligned across the longitudinal axis 48of the balloon catheter 20. The expansion of the balloon catheter 20 asa result of the filling is determinable by way of the strain gauges 46.The strain gauges are connected to the evaluation unit 36 and/or thecontrol unit 28 by way of a cable (not depicted here) such that theevaluation unit 36 or the control unit 28 can determine the expansion ofthe balloon catheter 20 on account of the modified resistances of thestrain gauges 46. If the expansion reaches a threshold, the control unit28 can reduce or stop the filling of the balloon catheter 20 or of thefirst chamber 20 a or the second chamber 20 b of the balloon catheter20.

The balloon catheter 20 shown in FIG. 2 has an egg-shaped form with twochambers separated from one another. Alternative embodiments maycomprise a multiplicity of further chambers, which are preferablyfillable separately from one another by way of an appropriate cathetertube 22. Depending on application, the outer form of the ballooncatheter 20 can also have a cylindrical or substantially planarembodiment. In addition or as an alternative to the use of strain gauges46, the balloon catheter 20 can have pressure sensors (not shown in thedrawings), which are arranged in the first chamber 20 a and/or in thesecond chamber 20 b in order to detect the respective chamber internalpressure. In a manner analogous to the strain gauges 46, the expansionof the balloon catheter 20 is automatically determinable by theevaluation unit 36 by way of the chamber internal pressure establishedby the pressure sensors in conjunction with information about theexpansion properties of the balloon catheter 20 and hence the fillingprocess can be subject to closed-loop control.

LIST OF REFERENCE SIGNS

10 Pointer

12 Instrument handle

14 Instrument shaft

16 Instrument sensor

18 Instrument tip

20 Balloon catheter

20 a First chamber

20 b Second chamber

22 Catheter tube

22 a First channel

22 b Second channel

24 Fluid compressor

26 Compressor cable

28 Control unit

30 Storage unit

32 Display unit

34 Display cable

36 Evaluation unit

38 Generator cable

40 Field generator

42 Electromagnetic field

44 Instrument cable

46 Strain gauges

48 Longitudinal axis

1. A medical system for assisting in planning and/or performing thereconstruction of usually symmetrical body parts of a patient,comprising: at least one measuring unit for measuring a first area and asecond area in order to establish a topography of the first area and thesecond area; a storage unit for storing the established topographies ofthe first area and the second area; an evaluation unit for establishinga mirror image of the stored topography of the first area and forcalculating deviations between the stored topography of the second areaand the mirror image of the stored topography of the first area; and acontrol unit for outputting guidance information for at least onemedical instrument on the basis of the calculated deviations in thetopography of the second area from the mirror image of the storedtopography of the first area in order to reconstruct the topography ofthe second area in accordance with the mirror image of the topography ofthe first area.
 2. The system as claimed in claim 1, wherein a datatransmission interface for transmitting the topography data of a surfaceestablished by the measuring unit to the evaluation unit and/or storageunit.
 3. The system as claimed in claim 1, wherein the at least onemeasuring unit comprises a mechanical sensing device for mechanicallysensing an area, wherein the mechanical sensing device can be integratedin a position detection system such that position data from a sensingtip of the sensing device are establishable by the position detectionsystem and displayable on a display unit.
 4. The system as claimed inclaim 3, wherein the mechanical sensing device comprises a pointer withan at least partly spherically shaped instrument tip.
 5. The system asclaimed in claim 1, wherein at least one measuring unit comprises anoptical sensing device for optically sensing an area.
 6. The system asclaimed in claim 5, wherein the optical sensing device comprises alaser, a video device and/or a photocell and wherein the image dataestablished by the optical sensing device are displayable on a displayunit.
 7. The system as claimed in claim 1, wherein at least one medicalinstrument is embodied as a balloon catheter which, in accordance withthe guidance information output by the control unit, is fillable with awork fluid.
 8. The system as claimed in claim 7, wherein the system hasat least one sensor for detecting the internal pressure and/or theextent of the balloon catheter.
 9. The system as claimed in claim 8,wherein the control unit is embodied to control the filling of theballoon catheter taking into account the data established by the sensor.10. The system as claimed in claim 9, wherein the control unit isconfigured to control a filling speed of the balloon catheter in amanner dependent on the respective extent and/or on the internalpressure of the balloon catheter, wherein the filling speed istendentiously intended to decrease with increasing extent or withincreasing internal pressure of the balloon catheter.
 11. The system asclaimed in claim 10, wherein the balloon catheter has a plurality ofchambers, wherein the chambers are fillable independently of oneanother.
 12. The system as claimed in claim 1, wherein the evaluationunit is configured to establish deviations in the topography of thesecond area from the mirrored topography of the first area on the basisof individual representative measurement points on the second area. 13.The system as claimed in claim 1, wherein the measuring unit is embodiedto establish the topography of the second area, at least atrepresentative measurement points, during the production orreconstruction of the second area.
 14. The system as claimed in claim13, wherein the control unit adapts the guidance information for atleast one medical instrument on the basis of the topography data of thesecond area established during the reconstruction of the second area.15. The system as claimed in claim 14, wherein the medical instrument isan active medical instrument, wherein the control unit is embodied tocontrol the operating state of the active medical instrument in a mannerdependent on the position of the active medical instrument from thetopography of the second area established by the control unit.
 16. Thesystem as claimed in claim 7, wherein the balloon catheter has aplurality of chambers, wherein the chambers are fillable independentlyof one another.